BRONCHIAL TUBES 



235 



The submucosa consists of loose areolar tissue which contains 

 many small tubulo-acinar mucous glands. The ducts of these 

 glands penetrate the mucosa and open upon the free surface of 

 the trachea. They supply an abundant 

 mucous secretion. This coat also contains 

 the larger blood vessels and nerves which 

 are destined for the supply of the mucosa. 



The fibre-cartilaginous coat is formed 

 by the C-shaped " ring cartilages " of the 

 trachea which are firmly united to one 

 another by ligamentous membranes of 

 fibrous tissue continuous with the peri- 

 chondrium of adjacent cartilage plates. 

 The cartilages are of the hyaline variety 

 and are subject to more or less ossification 

 as age advances. They rarely overlap each 

 other, so that but a single plate of carti- 

 lage forms the wall at any given point. 

 Their borders are irregular, and horizon- 

 tal sections near the upper or lower 

 margin of the cartilage, frequently pass 

 through several projections, which, unless 

 properly interpreted, would lead one to 

 infer that the cartilaginous ring was in- 

 complete. 



The interval between the ends of the C-shaped cartilage rings 

 is occupied by a membrane of smooth muscle whose transverse 

 fibres unite the adjacent ends of the cartilages. The muscle 

 fibres are inserted into the perichondrium of the cartilages. 

 Many of the fibres are obliquely, and a few of the outermost 

 are longitudinally disposed. This muscular portion of the tra- 

 cheal wall forms the so-called trachealis muscle. The mucous 

 membrane and submucosa of this portion of the trachea are 

 unusually thick and their mucous glands are exceptionally large. 

 The loose fibrous tissue which invests the outer surface of the 

 cartilaginous coat contains many small sympathetic nerve trunks 

 and ganglia. 



THE BRONCHIAL TUBES AND PULMONARY ALVEOLI. 

 At the root of the lung the trachea divides into a primary bronchus 

 for each lung. By repeated subdivisions the earliest branches 

 being given off at acute angles, the later ones at more obtuse 



FIG. 199. Mucus SECRETING, 



TUBULO-ALVEOLAB GLAND 

 OF THE HUMAN TKACHEAL 

 MUCOSA. 



Reconstruction, x 200. 

 ( After Maziaraki.) 



